Atomically controlled quantum chains hosting a Tomonaga-Luttinger liquid

Atom assemblies on surfaces represent the ultimate lower size limit for electronic circuits, and their conduction properties are governed by quantum phenomena. A fundamental prediction for a line of atoms confining the electrons to one dimension is the Tomonaga-Luttinger liquid(1). Yet, astonishingly, this has not been observed in surface systems so far. Here we scrutinize self-organized chains of single-atom width by scanning tunnelling spectroscopy and photoemission. The low-energy spectra univocally show power-law behaviour. Even more, the density of states obeys universal scaling with energy and temperature. This demonstrates paradigmatic Tomonaga-Luttinger liquid properties(2,3) encountered at the atomic scale, with bearing for the conductivity of wires and junctions. Local control enables us to study modified interactions due to defects or bridging atoms not previously possible.